1Field of the Invention
The present invention relates to the devices employed for joining together two successive sections of a conveyor belt.
2. Description of the Prior Art
A joint of this type is usually formed by fitting two complementary series of metallic belt-fasteners on the ends of the two sections to be joined together, then coupling these two series of fasteners by means of a hinge-pin which is passed through the entire set of interengaged hinge-knuckles of these fasteners. The connecting hinge-pin employed for this purpose must be flexible in order to ensure that the corresponding conveyor belt can assume an inwardly curved transverse profile and thus take the shape of a trough on the belt-supporting rollers.
In consequence, said coupling hinge-pin usually consists of a cable made up of twisted wires. However, the mechanical resistance to wear of a hinge-pin of this type is relatively limited.
During recent years, a certain number of very effective solutions have in fact been devised for increasing the mechanical strength of the hinge-knuckles of the belt-fasteners since these hinge-knuckles previously constituted a weak point of the coupling devices thus formed. In consequence, it is now the connecting hinge-pin itself which constitutes the weak point of the assembly. In fact, the rubbing friction with which the hinge-knuckles of the belt-fasteners are applied on the periphery of a hinge-pin of this type very rapidly results in failure of one of the twisted wires. From this moment onwards, the hinge-pin becomes unserviceable in a very short time.
Moreover, as soon as one of the twisted wires is broken, the ends of the two resulting segments tend to become detached from the other wires and to spread out, thus practically prohibiting any possibility of disassembly of the corresponding hinge-pin. Now in the case of coupling devices employed on conveyor belts of the type used in coal mines, the belt-coupling devices frequently have to be disassembled in order to increase the length of the conveyor belts by incorporating an additional belt section. When the hinge-pin of a belt-coupling device cannot be disassembled, this makes it necessary to cut the ends of the conveyor-belt on each side and to mount new belt-fasteners on the ends without any possibility of recovering the old fasteners.
In order to overcome these disadvantages, a certain number of solutions have already been proposed but none has proved satisfactory. Thus U.S. Pat. No. 2,962,782 and French Pat. No. 720,857 describe hinge-pins constituted by a cable of twisted wires on which is fitted a protective outer sheath of flexible material. However, this design concept simply ensures protection of the corresponding pin but does not result in higher mechanical strength.
In regard to German Pat. Nos. 926,645, No. 2,240,013 and No. 2,507,474, they describe a hinge-pin constituted by a cable formed of twisted wires over which are threaded a series of metal sleeves arranged in succession. A solution of this type is better than the previous design since the metal sleeves thus provided have higher mechanical strength than a simple protective sheath of flexible material.
However, this solution remains imperfect. In fact, since the presence of the covering sleeves makes it necessary to reduce the cross-section of the axial cable, this latter has insufficient resistance to elongation. In point of fact, as soon as this cable is subjected to elongation under the action of stresses, there results a possibility of play between covering sleeves. This in turn has the effect of baring the axial cable between two successive sleeves and consequently of causing damage to this latter in the form of rupture of one or a number of twisted wires of the periphery.
As soon as a rupture of this type takes place, disassembly of the hinge-pin is no longer possible. However, for reasons already explained earlier, such disassembly is essential in order to permit periodic mounting of an extension band of the conveyor-belt when this latter is employed in a coal mine.
Moreover, in the event of complete rupture of the cable at an intermediate point of its length, it is impossible to remove the constituent elements of this latter in order to place a new coupling pin in position. In fact, since the metal sleeves are independent of each other, withdrawal of both cable segments does not make it possible to extract with each segment the sleeves which had been placed on the two segments. In consequence, any repair of the belt-coupling device calls for a certain number of relatively complicated operations before it is possible to withdraw all the elements of the damaged coupling pin in order to replace this latter by a new pin.
It is in any case by reason of these various disadvantages that this solution has not been applied on an industrial scale.